Sen. Kirsten Gillibrand is seen in this undated photo. Photo Credit: Getty Images

WASHINGTON -- Sen. Kirsten Gillibrand lashed out at the Pentagon and the president Tuesday after her controversial measure on prosecuting military sexual assault won a Senate majority but fell short of the 60 votes needed to pass.

The junior Democratic senator from New York attacked the "Pentagon spin machine" for obscuring its lack of progress on curbing assaults and President Barack Obama for not addressing the issue after promising in 2013 that he would.

"We are not going away," Gillibrand said in a news conference with some of her bipartisan co-sponsors after the measure failed 50-49. "The vote is over but we are going back to our office to get ready for the next one."

Gillibrand's measure would fundamentally change how the U.S. military addresses sexual assault cases, shifting authority from commanders to attorneys to prosecute those crimes.

In December 2013, Obama gave the military a year to fix its handling of sexual assaults.

"If I do not see the kind of progress I expect, then we will consider additional reforms," he said then. But Gillibrand said Obama hasn't raised the issue again. "I expected more of him than that," she said.